Kloss's gibbon,
Mentawai gibbon, beelohHylobates klossii

This species is completely black. Animals differ
from other completely black gibbons by their smaller size and the absence of an external
throat sac (as compared to S. syndactylus) and by the absence of an occipital
crest (as compared to males of N. concolor or N. sp. cf. nasutus).

Adult male "Bilou", Twycross Zoo, England,
4 Oct. 1988.

Same adult male "Bilou", Twycross Zoo, England,
Jan. 2005 (photograph by Melissa Waller).
This male appears to have developped a brownish tinge, more fluffy fur and a broader
hairdo, as compared to the photograph on the left made almost 20 years earlier.